The invention is directed to improvements in a magnetic valve. Magnetic valves of many kinds are known, for performing manifold switching functions. Typically, they include a valve housing, an armature movably supported in it; an electric exciter coil for actuating the armature; and in the hydraulic portion controlled by the movement of the armature, the valve body, which forms the seat for the sealing element, such as a sealing ball; connecting means that couple the thus-embodied ball valve to the armature movement; and a biasing spring, which determines a specified switching state of the valve.
In the simplest case, the valve may be in the form of a 2/2-way valve, that is, a valve having a valve inlet and a valve outlet, which is movable into two switching positions, namely the closing and the opening position of the valve. Such 2/2-way valves are in fact often incorporated into the brake lines of motor vehicles, to achieve so-called ABS or anti-skid braking functions. In the closing position, they can prevent the delivery of additional hydraulic fluid to the wheel brake cylinders (in the maintaining function) and as needed, with further parallel-acting magnetic valves, may also enable a pressure drop, or upon a shift to the open position may permit a further pressure buildup.
The following discussion addresses the design and function of such a 2/2-way magnetic valve for achieving ABS functions, because this is also a preferred field for the use of the present invention. Since such ABS magnetic valves necessarily remain continuously in place in the brake lines, they must present the maximum possible flow cross section for the frequent case of normal braking, yet for ABS functions this feature is undesirable, since precisely in the ABS situation it is the primary purpose of the system to lower the brake pressure at first, so as to eliminate the tendency for the vehicle to skid, and then to maintain it as needed at a given level, then (gradually) build it up again, and so forth, with a rapid succession of commands issued by a central control system in response to wheel sensor signals.
Since typically a 2/2-way valve can be moved only either completely into the open position or completely into the closed position, for the time being disregarding the possibility of an incremental operation, a standard 2/2-way magnetic valve would therefore, upon receiving the control command "OPEN", shift entirely to the open position, with the large flow cross section that is desired for normal braking, and a correspondingly steep rise of pressure in the brake cylinders would ensue. This is often unfavorable for ABS control; on the other hand, such valves cannot function with a smaller cross section, or else time would be lost for the pressure buildup required should fast braking become necessary.